The change of major organic acid contents were examined in mackerel, pacific yellow croaker and brown sole on heating conditions. The organic acid contents of mackerel were the higher that the others. The content of lactic acid was the highest in all samples commonly and that of succinic acid was second level and these organic acids were over 95% of total organic acid. The content of ${alpha}-ketoglutaric$ acid was higher acid content was greater with higher heating temperature. Decreasing of organic acid content was higher at steamed and first heating than warmed and rewarmed.